Developing unit for electrostatic latent image

ABSTRACT

A developing unit comprises a developing box having an opening, which is brought into abutment against a surface on which an electrostatic latent image is formed, thereby forming a liquidtight developing chamber. A liquid developer is supplied into the developing chamber to develop the latent image. At least an inner wall of the developing box is formed by or coated with a liquidrepellent resin.

Umted States Patent 1 1 1111 3,898,957

Masumura Aug. 12, 1975 [54] DEVELOPING UNIT FOR ELECTROSTATIC 3,305,459 2/1967 Smith et a1 l18/D1G. 23

LATENT IMAGE 3,392,707 7/1968 Marx lls/DlG. 23

3,446,649 5/1969 Degenhardt et a1. 117/37 LE Inventor: Masao Masumura, y Japan 3,683,852 8/1972 Yamaguchi et a1 118/637 a I I 3,714,665 1 1973 MUISChlCI 346/74 ES [73] Tokyo Jdpm 3,776,630 12/1973 011110 et a1. 355/10 [22] Filed: Dec. 21, 1973 [21] Appl. No.1 427,212

[30] Foreign Application Priority Data Dec. 28, 1972 Japan 47-3473 [56] References Cited UNITED STATES PATENTS 2/1959 Hornbostel 118/D1G. 23 11/1966 Lehmann 118/637 X Primary Examiner-Mervin Stein Attorney, Agent, or FirmCooper, Dunham, Clark, Griffin & Moran 5 7 1 ABSTRACT A developing unit comprises a developing box having an opening, which is brought into abutment against a surface on which an electrostatic latent image is formed, thereby forming a liquid-tight developing chamber. A liquid developer is supplied into the developing chamber to develop the latent image. At least an inner wall of the developing box is formed by or coated with a liquid-repellent resin.

8 Claims, 6 Drawing Figures PATENTED AUG 1 2 I975 SHEET DEVELOPING UNIT FOR ELECTROSTATIC LATENT IMAGE BACKGROUND OF THE INVENTION The invention relates to a developing unit for electrostatic latent image.

When using a liquid developer to develop an electrostatic latent image formed on an electrophotographic copying member including a photoconductive material or an electrostatic recording member comprising an insulating resin (hereinafter referred to as recording member), it is advantageous to place the recorded surface on which the latent image is formed in an upright plane. A microphotograph can be produced, using the electrophotographic process, on a portion of an electrophotographic film material drawn from a roll and comprising an organic photoconductive material as its photosensitive layer. The film may be drawn from the roll with its photosensitive surface in an upright position to be subjected to charging and exposure. A developing box may then be brought into abutment with the surface on which an electrostatic latent image is formed, in such manner as to close the opening in the box with this surface to form a liquid-tight developing chamber, into which a liquid developer may be supplied for contact with the latent image for the purpose of developing it. Subsequently, the developer may be drained from the developing chamber, thereby leaving a microphotograph on the surface covering the opening in the developing box. However, when wet developing as described above is applied to an upright recording surface on which the latent image is formed, it is unavoidable that the some developing solution remains in the area of contact between the inner wall of the developing box and the surface of the recording member which is developed, when the developing solution is drained from the interior of the developing box. Such residue advantageously mars the image surface of the recording member.

SUMMARY OF THE INVENTION It is an object of the invention to provide a developing unit for electrostatic latent images in which liquidrepellent resin is used in a manner to avoid the above described disadvantage occurring in prior art developing units of the type in which a liquid developer is applied to an upright surface to be developed.

In accordance with the invention, at least one inner wall of the developing box is formed by or coated with liquid-repellent resin material to prevent the developing solution from remaining within the developing chamber when the developing solution is displaced therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a system including a developing unit to which the invention can be applied;

FIG. 2 is a section of the developing unit shown in FIG. 1 to which the invention is applied;

FIG. 3 is a section of a developing unit in which the invention is not applied;

FIG. 4 is a plan view of a film surface developed with the developing unit of FIG. 3;

FIG. 5 is a cross section of the developing unit according to the invention; and

FIG. 6 is a plan view of a film surface developed with the developing unit of FIG. 5.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, a system including a developing unit to which the invention can be applied will be initially described. There is shown a roll 1 of elongate microphotograph film la, with its photosensitive surface which may comprise a layer of organic photoconductive material placed inside. A portion of the film is drawn from the roll I, wound counterclockwise around half the periphery of a guide roller 2, and also wound clockwise half the periphery of a feed drum 3 to be fed onto a pressure plate 4 to be held thereon in an upright position. The pressure plate 4 is carried by a slide member 5 which is movable in the direction indicated by an arrow a and thus in a direction perpendicular to the length of the film held tensioned. When conveying the film, the pressure plate 4 is retracted from the film 1a, and when the film is stationary for the purpose of applying electrophotographic processings, the pressure plate 4 is advanced to bear against the rear surface of the film la so as to maintain the planarity thereof. A charger (not shown) is initially passed by the photosensitive surface of the film 1a held on the pressure plate, thereby charging the surface. Then an exposure unit (not shown) is brought into alignment with the area of the film on the pressure plate so as to provide an imagewise exposure of the charged photosensitive surface. Subsequently, a developing box 6 is moved toward the exposed photosensitive surface, and an opening 60 therein is brought into abutment with the photosensitive surface. Thereupon, the opening 6a of the developing box 6 is covered by the exposed photosensitive surface or the surface lb on which the electrostatic latent image is formed (see FIG. 2), thereby providing a liquid-tight developing chamber. The developing box 6 is provided with a developing solution supply inlet 6b at its top and also with a developing solution drainage port 60 at its bottom. Additionally, the developing box is formed with a reentrant portion 6d on which a counter electrode plate 7 is attached which is connected to ground potential. As shown in FIG. 2, the inner walls of the developing box 6 which extend from the top wall and from the bottom wall toward the opening 6a, respectively, are formed as ramp wall surfaces to facilitate the flow of a liquid developer supplied through the inlet 6b toward the opening 6a and also the flow of the developing solution within the box toward the drainage port 66 upon displacing the developing solution therefrom.

A liquid developer 8 is supplied through the inlet 6b into the developing chamber which is formed in a liquid-tight manner. Of course, the drainage port 60 is closed by a valve 9 at this time. The supply of the developer 8 should be sufficient to fill the interior of the developing chamber. As a result, the electrostatic latent image formed on the photosensitive surface lb contacts the developer 8 to be developed thereby into a visible image. Upon completion of the developing process, the valve 9 is opened to drain the developing solution from the chamber through the port 6c.

However, when displacing the developing solution is drained, it is not completely displaced from the interior of the developing chamber, but remains as liquid drops on the inner wall of the developing box 6, as shown in FIG. 3, and also remains as residue in the area of Contact between the developed surface lb and the developing box 6. Such residue 80 mars the developed image.

Generally, a recording member comprising a layer of organic photoconductive material will permit little penetration of the developing solution into the photosensitive layer as in an Electrofax paper comprising ZnO or the like, and thus a relatively long period of time is required for drying. The drying process is of significance particularly when an image of high resolution is to be produced, and when the drying is insufficient, a blotting or spreading will occur in the toner of the image, causing an inversion to degrade the quality of the resulting microphotograph.

The presence of residue 8a within the developing box causes such residue to attach to the developed image surface 1c (see FIG. 4) to mar it, When the film is fed by an increment, such residue 8a will produce a streak of developing solution to mar the image surface lc of the next frame.

In accordance with the invention, liquid-repellent resin is applied to the inner wall of the developing box 6 in the form of stratum or strata, as indicated in FIGS. 2 and 5. Such liquid-repellent resin 10 is applied in particular to those ramp surface portions which extend from the top wall and from the bottom wall of the box to the opening 6a, respectively. The liquidrepellent resin may comprise polytetrafluoroethylene (for example, polyflon dispersion D-l, a trade mark of Japanese corporation Daikin); polytrifluorochloroethylene; or polymers or copolymers of vinyl fluoride, vinylidene fluoride, dichlorodifluoroethylene or the like, and may be applied to the inner wall as a stratum. Alternatively, a liquid-repellent metal complex compound, for example, [CF (CF ),,CO C- r OH]* 4Cl' (a product of Japanese corporation Sumitomo-3M with a trade mark Scotchban FC-805) may be coated as a stratum. It is found that fluorinecontaining compound is effective for this purpose.

When a liquid-repellent resin 10 is applied on the inner wall of the developing box 6, the displacement of the developing solution 8 takes place in a smooth manner upon draining without leaving any substantial amount thereof within the developing chamber. Any residue of the developer will be in the form of a relatively large-sized drop 8b situated at one location near the drainage port 6c, as shown in FIG. 5, and it is a simple matter to displace such drop residue. As a consequence, no residue of developing solution 81) will attach to the developed image surface 1c (FIG. 6), thus leaving it in a clean condition.

Experiments have been conducted using a film which comprised an organic photoconductive material such as polyvinyl carbazole added with a certain amount of sensitizing dye and plasticizer. The organic photoconductive material has been applied on a transparent film base which may comprise polyester or the like, to a thickness of about 10 microns, with a conductor such as copper iodide, tin oxide or the like and a layer of adhesive interposed therebetween. Subsequent to the charging and exposure of the film, the latent image thereon was developed with a developing solution which comprised a dispersion of toner (M.R.P. toner made by Ricoh) having a negative polarity in a highly resistive solvent (ISOPAR H made by Esso Standard).

EXAMPLE 1 (control) Using the above mentioned electrophotographic film, the conductor has been connected to the ground, and a corona discharge was applied from a discharge electrode located opposite to the photosensitive surface, charging the photosensitive surface to a surface potential of +800 volts. Subsequently, an exposure was made through an optical lens at the level of lux.- sec., using conventional letters of a resolution chart, prepared by Microphotograph Association of Japan. A developing box having an opening defined by a frame which is Alumirite processed was brought into abutment against the exposed surface, and the above mentioned developing solution was used to develop the la tent image, followed by drying to produce an image. The resulting image was marred, stained with patterns indicative of insufficient drying around its periphery.

EXAMPLE 2 The same procedure as in Example 1 was repeated to form an electrostatic latent image on the film, which was developed using a developing box having the liquid-repellent resin material applied to its interior and to the frame of the opening. In this example, experiments have been conducted applying each one of the following liquid-repellent resins to the inner wall as a stratum:

l, Polytetrafluoroethylene;

2. Polytrifluorochloroethylene;

3. Copolymer of vinyl fluoride and vinylidene fluoride; and

4. [CF (CF ),,CO Cr OH] 4C1' (a product of Japanese corporation Sumitomo-3M with a trade mark Scotchban FC-805). Subsequent to the displacement of the developing solution, very little wetting was observed in the interior of the developing box as well as on the frame surface, and it was recognized that the residue was readily drained in the form of large drops. The image obtained subsequent to the drying was very very clean in contrast to that obtained in Example 1.

While in the above description, the liquid-repellent resin 10 was applied, by baking or coating, in the form of strata on the inner wall of the developing box 6, it should be apparent that the developing box itself may be moulded from such liquid-repellent resin with an equal capability of completely removing residue of the liquid developer.

What is claimed is:

l. A developing unit for electrostatic latent images of the type in which a recording member having an electrostatic latent image formed thereon is held in an upright position and in abutment with an opening in a developing box to thereby form a liquid-tight developing chamber, into which a liquid developer is supplied to develop the latent image on the recording member and is then displaced from the interior of the developing chamber upon completion of the developing process, including the improvement wherein the developing box comprises:

an interior access area at least the bottom portion of which inclines downwardly from the lower edge of said opening; and

a liquid-developer-repellent resin material forming the surface of said bottom portion and the lower ride, vinylidene fluoride and/or dichlorodifluoroethylene.

6. A developing unit according to claim 2 in which the fluorine-containing polymerized compound comprises [CF (CF ),.CO Cr Ol-l] 4Cl.

7. A unit as in claim 1 wherein said interior access area further comprises an upper portion inclined upwardly from the upper edge of said opening and the surface of said upper portion comprises a liquid developer-repellent resin material.

8. A unit as in claim 1 wherein the entire surface of the interior access area comprises a liquid-developerrepellent resin material. 

1. A developing unit for electrostatic latent images of the type in which a recording member having an electrostatic latent image formed thereon is held in an upright position and in abutment with an opening in a developing box to thereby form a liquidtight developing chamber, into which a liquid developer is supplied to develop the latent image on the recording member and is then displaced from the interior of the developing chamber upon completion of the developing process, including the improvement wherein the developing box comprises: an interior access area at least the bottom portion of which inclines downwardly from the lower edge of said opening; and a liquid-developer-repellent resin material forming the surface of said bottom portion and the lower edge of said opening to facilitate the displacement of the developer therefrom.
 2. A developing unit according to claim 1 in which the liquid-developer-repellent resin material comprises fluorine-containing polymerized compound.
 3. A developing unit according to claim 2 in which the fluorine-containing polymerized compound comprises polytetrafluoroethylene.
 4. A developing unit according to claim 2 in which the fluorine-containing polymerized compound comprises polytrifluorochloroethylene.
 5. A developing unit according to claim 2 in which the fluorine-containing polymerized compound comprises a polymer or copolymer comprising vinyl fluoride, vinylidene fluoride and/or dichlorodifluoroethylene.
 6. A developing unit according to claim 2 in which the fluorine-containing polymerized compound comprises (CF3(CF2)nCO2Cr2OH)4 4Cl .
 7. A unit as in claim 1 wherein said interior access area further comprises an upper portion inclined upwardly from the upper edge of said opening and the surface of said upper portion comprises a liquid-developer-repellent resin material.
 8. A unit as in claim 1 wherein the entire surface of the interior access area comprises a liquid-developer-repellent resin material. 